Abstract
Abstract. Biological diversity is inextricably linked to community stability and ecosystem functioning, but our understanding of these relationships in freshwater ecosystems is largely based on short-term observational, experimental, and modelling approaches. Using a multidecadal diatom record for the past ca. 16 000 years from Lake Baikal, we investigate how diversity and palaeoproductivity have responded to climate change during periods of both rapid climate fluctuation and relative climate stability. We show dynamic changes in diatom communities during the past 16 000 years, with decadal shifts in species dominance punctuating millennial-scale seasonal trends. We describe for the first time in Lake Baikal a gradual shift from spring to autumnal diatom communities that started during the Younger Dryas and peaked during the Late Holocene, which likely represents orbitally driven ecosystem responses to long-term changes in seasonality. Using a multivariate classification tree, we show that trends in planktonic and tychoplanktonic diatoms broadly reflect both long-term climatic changes associated with the demise of Northern Hemisphere ice sheets and abrupt climatic changes associated with, for example, the Younger Dryas stadial. Indeed, diatom communities are most different before and after the boundary between the Early and Middle Holocene periods of ca. 8.2 cal kyr BP, associated with the presence and demise of Northern Hemisphere ice sheets respectively. Diatom richness and diversity, estimated using Hill's species numbers, are also shown to be very responsive to periods characterized by abrupt climate change, and using knowledge of diatom autecologies in Lake Baikal, diversity trends are interpreted in terms of resource availability. Using diatom biovolume accumulation rates (BVARs; µm3 cm−2 yr−1), we show that spring diatom crops dominate palaeoproductivity for nearly all of our record, apart from a short period during the Late Holocene, when autumnal productivity dominated between 1.8–1.4 cal kyr BP. Palaeoproductivity was especially unstable during the Younger Dryas, reaching peak rates of 18.3 × 103 µm3 cm−2 yr−1 at ca. 12.3 cal kyr BP. Generalized additive models (GAMs), which explore productivity–diversity relationships (PDRs) during pre-defined climate periods, reveal complex relationships. The strongest statistical evidence for GAMs were found during the Younger Dryas, the Early Holocene, and the Late Holocene, i.e. periods of rapid climate change. We account for these differences in terms of climate-mediated resource availability, and the ability of endemic diatom species in Lake Baikal to adapt to extreme forms of living in this unique ecosystem. Our analyses offer insight into how productivity–diversity relationships may develop in the future under a warming climate.
Highlights
Understanding the role that biological diversity plays in ecosystem stability and function is an important challenge in ecological research (Tilman et al, 1997; McCann, 2000; Loreau et al, 2001; Isbell et al, 2015; Hagen et al, 2021)
This study provides important insights into our understanding of productivity–diversity relationships (PDRs) in aquatic ecosystems
We show that diatom communities and palaeoproductivity are sensitive to extrinsic drivers of climate change
Summary
Understanding the role that biological diversity plays in ecosystem stability and function is an important challenge in ecological research (Tilman et al, 1997; McCann, 2000; Loreau et al, 2001; Isbell et al, 2015; Hagen et al, 2021). Our understanding of productivity–diversity relationships (PDRs) is largely based on short-term observational (Dodson et al, 2000; Ptacnik et al, 2008; Korhonen et al, 2011), experimental (McGrady-Steed et al, 1997; Interlandi and Kilham, 2001; Winfree et al, 2015), and modelling approaches (Aoki, 2003), with very few long-term studies undertaken (Rusak et al, 2004) This constitutes an important gap in our knowledge because in terms of climate change, productivity–diversity relationships and resource use efficiency (Gross and Cardinale, 2007; Ptacnik et al, 2008) will be fundamentally different over long (e.g. climate and landscape evolution) and short (e.g. pulse disturbances such as climate disturbance events; Kéfi et al, 2019) timescales
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